stopped when we commence to look in the direction of such a theory with the
cynical question, What do you mean by explaining a property of matter? As
to being stopped by any such question, all I can say is that if engineering
were to be all and to end all physical science, we should perforce be
content with merely finding properties of matter by observation, and using
them for practical purposes. But I am sure very few, if any, engineers are
practically satisfied with so narrow a view of their noble profession. They
must and do patiently observe, and discover by observation, properties of
matter and results of material combinations. But deeper questions are
always present, and always fraught with interest to the true engineer, and
he will be the last to give weight to any other objection to any attempt to
see below the surface of things than the practical question, Is it likely
to prove wholly futile? But now, instead of imagining the question, What do
you mean by explaining a property of matter? to be put cynically, and
letting ourselves be irritated by it, suppose we give to the questioner
credit for being sympathetic, and condescend to try and answer his
question. We find it not very easy to do so. All the properties of matter
are so connected that we can scarcely imagine one _thoroughly explained_
without our seeing its relation to all the others, without in fact having
the explanation of all; and till we have this we cannot tell what we mean
by "explaining a property" or "explaining the properties" of matter. But
though this consummation may never be reached by man, the progress of
science may be, I believe will be, step by step toward it, on many
different roads converging toward it from all sides. The kinetic theory of
gases is, as I have said, a true step on one of the roads. On the very
distinct road of chemical science, St. Claire Deville arrived at his grand
theory of dissociation without the slightest aid from the kinetic theory of
gases. The fact that he worked it out solely from chemical observation and
experiment, and expounded it to the world without any hypothesis whatever,
and seemingly even without consciousness of the beautiful explanation it